1. Field of the Invention
The present invention relates to an electrophotographic photoreceptor, and to a process cartridge and an electrophotographic image forming apparatus using the eletrophotographic photoreceptor. More particularly the present invention relates to an electrophotographic photoreceptor suitable for image writing light having a wavelength of 350 to 400 nm emitted by a light source (hereinafter referred to as a xe2x80x9cwriting light sourcexe2x80x9d) such as laser diodes or light emitting diodes.
2. Discussion of the Background
So far, as photosensitive materials for photoreceptors used for electrophotographic image forming methods, various inorganic and organic photosensitive materials have been used. At this point, the xe2x80x9celectrophotographic image forming methodxe2x80x9d mentioned herein means an image forming process of the so-called Carlson process. The electrophotographic image forming method typically includes the following processes:
(1) a photosensitive photoreceptor is charged, for instance, using corona discharging in a dark place;
(2) the photoreceptor is exposed to imagewise light to selectively decay the charge on the lighted parts of the photoreceptor, resulting in formation of an electrostatic latent image; and
(3) the electrostatic latent image is developed with a toner including a colorant (e.g. dyestuffs and pigments), a polymer, etc. to form a visual image on the photoreceptor.
Photoreceptors using an organic photosensitive material have advantages of having good flexibility in designing a photoreceptor having good photosensitivity to image writing light used, good film formability, good flexibility, high film transparency, good mass productivity, less toxicity, low cost, etc. against photoreceptors including an inorganic photosensitive material. Therefore, organic photosensitive materials are used for almost all the photoreceptors now. In electrophotographic methods and similar processes, photoreceptors are required to have good electrostatic characteristics such as high photosensitivity, appropriate electric potential, high potential retainability, high potential stability, low residual potential and high photosensitivity over a broad wavelength range.
Recent progress of information processing systems using this electrophotographic image forming method is remarkable. Especially, progress of printers using a digital recording method in which information having been converted into digital signals is reproduced using light is remarkable in printing qualities and reliabilities. Such digital recording methods are applied not only to printers but also to ordinary copiers. Thus, digital copiers have been developed. Since various information processing functions can be added to digital copiers, it is considered that the demand for these digital copiers increases more and more.
As writing light sources applicable to the digital recording methods, small, inexpensive and reliable laser diodes (hereinafter referred to as xe2x80x9cLDxe2x80x9d) and light emitting diodes (hereinafter referred to as xe2x80x9cLEDxe2x80x9d) which emit light having a wavelength of from about 600 to 800 nm are typically used. The wavelength of light emitted by LDs typically used at present is 780 to 800 nm (i.e. a near infrared region).
At present, as the electrophotographic photoreceptor used for the electrophotographic image forming methods, functionally-separated multi-layer photoreceptors having a charge generation layer on a conductive support and a charge transport layer on the charge generation layer are typically used. In addition, for improving mechanical or chemical durability of the photoreceptors, a protection layer is sometimes formed on the surface of the photoreceptors. As for these functionally-separated multi-layer photoreceptors, when a photoreceptor with a charged surface is exposed to light, the light passes through the charge transport layer and is then absorbed in the charge generation material in the charge generation layer. The charge generation material generates charge carriers by absorbing light. The thus generated charge carriers are injected into the charge transport layer. The charge carriers are transported along an electric field formed by charges on the charge transport layer, resulting in neutralization of the charges of the photoreceptor. Thus, an electrostatic latent image is formed on the surface of the photoreceptor.
In order to impart high sensitivity to such a functionally-separated multi-layer photoreceptor, a combination of a charge generation material mainly having absorption in near infrared to visible regions and a charge transport material having absorption in yellow to ultraviolet regions, which does not prevent transmission of absorbed light toward the charge generation material (i.e., hardly causes masking effects (filtering effects) of writing light) is typically used.
In addition, using such a charge transport layer which does not absorb writing light is important to impart not only high sensitivity but also good charge stability and high image resolution to the photoreceptor. When a charge transport material absorbs writing light, it is known that various photochemical reactions are caused in the photoreceptor.
It is reported by J. Pacansky, et al., in Chem. Mater., 3,912(1991) that when a 4-diethylaminobenzaldehydediphenylhydrazone in a photosensitive layer serving as a charge transport material absorbs light, this compound is changed into an indazole derivative by a ring forming reaction, resulting in an increase of residual potential of the photoreceptor. In addition, it is reported in a thesis of T. Nakazawa, Osaka University (1994) that when a carbazolealdehydediphenylhydrazone derivative absorbs light, a geometric isomerism changes from an anti form to a syn form is made. It is also reported therein that the photosensitivity thereof changes and the residual potential increases because the ionizing potentials of the anti form and syn form are different.
Further, it is reported at page 165 in Japan Hardcopy"" 91 thesis that when some charge transport materials absorb light, the materials achieve a photo-excited state and are then deactivated, emitting strong fluorescent lights. It is also reported that the fluorescent light emitted by a charge transport material in a photosensitive layer is partly scattered from the surface of the photosensitive layer, but is mostly closed inside of the photosensitive layer and repeats multi-reflections in the photosensitive layer until it is completely absorbed by one or more materials included in the photosensitive layer. Thus, fluorescent light repeats reflections in the photosensitive layer until it is completely absorbed, and therefore a blurred image is produced, resulting in deterioration of image resolution.
In addition, it is disclosed in Japanese Laid-Open Patent Publication No. 55-67778 that using light having a wavelength as image writing light for a photoreceptor, which the charge transport layer of the photoreceptor absorbs, deteriorates the charge properties of the photoreceptor and increases the residual potential thereof when the photoreceptor is repeatedly used.
Thus, it is known that light absorption by a charge transport material adversely affects not only photosensitivity of the photoreceptor but also charge stability thereof and resolution of latent images formed thereon.
As the charge transport materials for use in electrophotographic photoreceptors, the following compounds have been disclosed.
(1) Triphenylamine compounds (U.S. Pat. No. 3,180,730); (2) benzidine compounds (U.S. Pat. No. 3,265,496 and Japanese Patent Publication No.58-32372); (3) stilbene compounds (Japanese Laid-Open Patent Publication No.58-65440); (4) xcex1-phenylstilbene compounds (Japanese Laid-Open Patent Publication No. 59-216853); (5) aminobiphenyl compounds (Japanese Laid-Open Patent Publication No. 1-280763); (6) 1,1 bis(p-diethylaminophenyl)-4,4-diphenyl-1,3-butadiene compounds (Japanese Laid-Open Patent Publication No. 62-30255); (7) 5-benzylidene-5H-dibenzo [a,d] cycloheptene compounds (Japanese Laid-Open Patent Publication No. 63-225660); (8) hydrazone compounds (Japanese Laid-Open Patent Publications Nos. 58-159536 and 59-15251); and (9) fluorene compounds (Japanese Laid-Open Patent Publication No. 2-230255). These compounds have light absorption in a wavelength range of from about 350 to 500 nm. Namely, these compounds hardly absorb light having a longer wavelength than the above-mentioned wavelength. Therefore, in an electrophotographic image forming method using a conventional LD or LED which emits light having a wavelength of from about 600 to 800 nm for writing images, the above-mentioned problems concerning performances of the charge transport compounds do not occur. Thus such charge transport compounds are widely used because of having high photosensitivity and stability.
However, lately, as a light source for digital recording methods, LDs (short wavelength LDs) and LEDs which emit light having a wavelength of from 400 to 450 nm (i.e., violet to blue light) have been developed and marketed.
When such a LD which emits light having about a half wavelength of that of a conventional near infrared LD is used as a writing light source for a laser scanner head, it is theoretically possible to make the spot diameter of the laser beam on a photoreceptor considerably small as can be understood by the following formula:
dxe2x88x9d(xcfx80/4)(xcexf/D)xe2x80x83xe2x80x83(1) 
wherein d represents the spot diameter of the laser formed on the photoreceptor; xcex represents the wavelength of the laser; f represents the focal distance of the fxcex8lens used; and D represents the lens diameter. Therefore, these short wavelength LDs are very useful for improving image recording density (i.e., image resolution).
In addition, when such a short wavelength LD or LED is used for optical systems of image forming apparatus, a compact and high speed image forming apparatus can be provided. Therefore, a need exists for a stable photoreceptor which has a sensitivity to light having a wavelength of from 400 to 450 nm.
However, the above-mentioned charge transport compounds absorb light having a wavelength of from 350 to 500 nm. According to the study of the present inventors, when a LD or a LED emitting light in this wavelength range is used as a light source for writing images on a photoreceptor, big problems occur such that the photosensitivity of the photoreceptor deteriorates, the residual potential increases and image resolution is decreased (i.e., blurred images are produced).
Accordingly, an object of the present invention is to provide an electrophotographic photoreceptor that can be stably used and produces images having high resolution even when a LD or a LED emitting light having a wavelength of from 350 to 500 nm is used as a light source.
Another object of the present invention is to provide an image forming apparatus and a process cartridge which can stably produce high resolution images using light having a wavelength of from 350 to 500 nm.
Briefly these object and other objects of the present invention as hereinafter will become more readily apparent can be attained by an electrophotographic photoreceptor including a photosensitive layer including a deactivating agent. The deactivating agent preferably has a charge transportability.
In another aspect of the present invention, an electrophotographic image forming apparatus is provided, which includes the above-mentioned electrophotographic photoreceptor, a charger, a light irradiator using a LD or a LED which emits light having a wavelength of from 350 to 500 nm as a light source, an image developer and an image transfer. The wavelength of the light emitted by the LD or the LED is preferably 400 to 450 nm.
In yet another aspect of the present invention, a process cartridge is provided, which includes the above-mentioned electrophotographic photoreceptor and at least one device selected from the group consisting of a charger, an image developer and a cleaner cleaning the photoreceptor and can be detachably set in an electrophotographic image forming apparatus.
These and other objects, features and advantages of the present invention will become apparent upon consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings.